Visible light is a part of the electromagnetic spectrum that can be perceived by human eyes. Infrared light is an electromagnetic wave (light) having a longer wavelength than the visible light. Studies have shown that infrared light can “penetrate” into human skin and is absorbable by the epidermis, dermis and subcutaneous tissue. At the same time, some spectrums absorbable by human organs falls within a visible range of electromagnetic spectrum, however, the reflected spectrum is a broadband reflection spectrum, which is within ranges of near-infrared light and red visible light. For instance, in a human brain, protein and oxyhemoglobin have an absorption spectrum and a reflection spectrum of 450 nm-600 nm and 700 nm-900 nm, respectively.
Therefore, organs can be detected according to the light spectrum absorbed or reflected by the different organs of the human body, for instance, for analyzing haemoglobin content, oxygen saturation, scattering lipid content, etc., and an extension has been made to the field of food or polymer component detection. In recent years, an optoelectronic component capable of generating a wide infrared emission spectrum has been widely used in security camera, iris/facial recognition, virtual reality, gaming notebook and light detection and ranging (LIDAR) technologies.
However, the infrared light emitted by optoelectronic components on the current market has disadvantages such as narrow emission spectrum, low radiant flux and the like, which cannot meet application requirements of the above medical component detection, intelligent technology and the like.
A luminescent material is a material that releases energy in the form of emitted light due to excitation from excitation light source. Currently, the luminescent material that is most studied and well-developed is mainly phosphor, especially phosphor excited by the blue chip for generating white LEDs, and the research has a focus on how to obtain emitted light (or called a secondary radiation) of a narrower wavelength range. The principle of white LED applies to the infrared phosphors converted LED also and hence it possesses advantages like low power consumption, compact, high lifetime and cheaper as compared to traditional light sources. In recent research, it is also reported that the use of phosphor is expanded to the security of anti-counterfeit and marker identification. For instance, it is reported that a study is made on the possibility of La3Ga5GeO14: Cr3+ for the applications of persistent luminescence, which mainly utilizing the phosphorescence property of the phosphors, continuous emission of light for a long time after excitation is ceased off. However, there is no report about the phosphor which can produce wide red visible light and near-infrared spectrums when excited by blue visible light, purple visible light or ultraviolet light and has a high radiant flux, let alone its application in the optoelectronic component.